The use of a fluorescent substance to convert the wavelength is widely known in the field of a light-emitting diode (LED) (Patent Literature 1). On the other hand, silicone resins have attracted attention as a material for covering an LED device for encapsulation and protection since it shows excellent light-resistance (Patent Literature 2).
In a white LED, fluorescent substances are generally dispersed in the vicinity of a chip to convert a blue light into a pseudo white light by a method of covering an LED chip with a silicone resin or an epoxy resin in which a fluorescent substances are dispersed and so on.
The fluorescent substances, however, have to be dispersed uniformly in the covering resin layer to make uniform white light since color drift is liable to occur when the fluorescent substances are dispersed ununiformly or unevenly in the resin layer. Accordingly, various methods have been investigated including screen printing and a method in which fluorescent substances are dispersed by sedimentation. These methods, however, have problems of complicating the manufacturing process and failing to obtain sufficient stability. Accordingly, it has been demanded for a convenient technology that can disperse fluorescent substances uniformly on the surface of a chip.
In LEDs and so on, the resin layer to cover the LED device is required to have high heat resistance and ultraviolet light resistance. Due to recent shifting to shorter wavelength and higher power of LEDs, addition curable silicone resins as in Patent Literature 3 have become insufficient in heat resistance and ultraviolet light resistance. This is because the addition curable silicone resin gives a cured silicone resin that contains a silmethylene bond (Si—CH2—CH2—Si) in the main chain skeleton. In shorter wavelength UV-LED, degradation of this silmethylene bond is accelerated particularly. This causes a problem markedly in a transparent encapsulating layer for transmitting UV light without using a fluorescent substance. To solve the foregoing problem, a condensation curable silicone resin has been proposed in which the main chain skeleton only contains siloxane bonds (Si—O—Si). With the lower reactivity, however, the condensation curable polyorganosiloxane is inferior to the addition curable polyorganosiloxane in productivity. The use of large amount of condensation catalyst to improve the reactivity accelerates the degradation of silicone resin, thereby failing to exhibit high heat resistance and light resistance that are intrinsic to silicon resins. Many of the catalysts are inappropriate for the fields in which transparency is important because the catalyst itself is colored or assumes a color by degradation.